Light itself are a form of electromagnetic waves that are emitted by a light source. A single light source usually emits electromagnetic waves of different shapes and orientation – for example, the light emitted by a projector moves into a specific direction while the electromagnetic waves move up and down or left and right along that direction.

Polarization filters also called polarizers are optical instruments that work like an „optical fence“ – they only permit light of a defined orientation to pass. If non-polarized light hits a polarizer, only those light waves that are in alignment with the optical fence are allowed to pass through. All other light is filtered out. The light that has passed the filter is called polarized and all light waves oscillate in along a single plain.

Thus, if a polarization filter is turned by 90 degrees, light that was able to pass through it before is blocked and other light waves can now pass the filter.

In the case of passive 3D stereo projections, polarizers are mounted on the projectors such that the orientation of the polarization of the filters is orthogonal to each other (i.e. at an angle of 90 degrees). The same applies to the 3D stereo glasses worn by the spectator. The polarization of the glasses is identical to the polarization angle of the filters mounted on the projectors. This is how passive 3D stereo projections ensure that the left eye only sees the picture projected by the left projector and vice versa.

Whenever polarizers are used, some of the light of the projector is blocked from reaching the screen. Thus these filters always reduce the brightness of the projection. In general the following holds: The higher the degree of the transmission of the polarizer, the brighter the projection of the picture. Leveraging coated filters is advantageous – they not only improve transmission but also help conserve the longevity of the projector lamps.

Advantages of linear polarization filters::

• Affordable
  
• Very good separation of the channels (e,g, left eye only seeing left picture)
  
• Best results when using high transmission polarization filters
  

Disadvantages of linear polarization filters:

• Separation of channels is compromised if spectators lilt their heads as this disturbs the alignment of the polarization of the projector and the glasses.
  Significant loss of brightness of the projection if poor quality filters are used.
  
• A non-depolarizing silver screen is required for front projection. In other words, the screen must not change the polarization of the reflected light.
  
• For rear projection screens or rear projection foils one also has to use non-depolarizing material.
  

Product links
3D Poliarizers